In general, a wheel bearing, which is used for a vehicle, serves to mount a vehicle wheel to a vehicle body so that the vehicle wheel of the vehicle may smoothly rotate without a frictional loss.
Further, a power transmission device for a vehicle, which transmits power produced by an engine of the vehicle to the vehicle wheel, typically has a constant velocity joint.
When the vehicle rebounds while traveling or the vehicle turns, the constant velocity joint serves to smoothly transmit power of the engine to the vehicle wheel while absorbing displacement in a diameter direction, displacement in an axial direction, or displacement of moment of force from the vehicle wheel.
Recently, fuel economy of the vehicle is required to be improved so as to save resources and reduce emission of pollutants. To meet these requirements, there is proposed a power transmission structure of the power transmission device for a vehicle in which the constant velocity joint is connected directly to the wheel bearing for rotatably supporting the vehicle wheel in order to improve assembly properties and maintainability as well as weight reduction.
FIG. 1 illustrates an example of a drive wheel bearing in which a constant velocity joint is integrally and rotatably coupled to a wheel bearing so as to correspond to the aforementioned power transmission structure.
A constant velocity joint 20 is penetratively inserted into a wheel bearing 10, and the wheel bearing 10 and the constant velocity joint 20 are integrally and rotatably coupled by means of a spline 30.
The wheel bearing 10 includes a wheel hub 12 which is integrally and rotatably fastened to a non-illustrated vehicle wheel, an outer race 14 which is positioned radially outside the wheel hub 12 so as to rotatably support the wheel hub 12 and fastened to and supported by a fixing body such as a vehicle body or a knuckle, an inner race 16 which is integrally and rotatably mounted to the wheel hub 12 by being fitted with an outer circumferential surface of the wheel hub 12, and rolling elements 18 which are interposed between the wheel hub 12 and the outer race 14 and between the inner race 16 and the outer race 14 and enable the wheel hub 12 and the inner race 16 to rotate relative to the outer race 14.
The constant velocity joint 20 penetrates the wheel hub 12, and is integrally and rotatably coupled to the inner circumferential surface of the wheel hub 12 by means of the spline 30. Further, a locking nut 40 is coupled to an axially outer tip portion of the constant velocity joint 20 in order to prevent the wheel hub 12 and the constant velocity joint 20 from being separated in the axial direction.
The spline 30 include teeth and tooth grooves circumferentially, alternately, and continuously formed on an outer circumferential surface of a shaft portion of the constant velocity joint 20 which is mounted to the wheel hub 12 by being fitted with the wheel hub 12. Further, the spline 30 include teeth and tooth grooves alternately and continuously formed on an inner circumferential surface of the wheel hub 12 with which the shaft portion of the constant velocity joint 20 is fitted.
Therefore, when the teeth of the constant velocity joint 20 are inserted into and coupled to the tooth grooves of the wheel hub 12, and the teeth of the wheel hub 12 are inserted into and coupled to the tooth grooves of the constant velocity joint 20, the wheel hub 12 and the constant velocity joint 20 are coupled to be integrally rotatable in the circumferential direction through the engagement between the teeth and the tooth grooves.
Therefore, rotational power of the engine is transmitted to the vehicle wheel via the constant velocity joint 20 through the wheel hub 12 of the wheel bearing 10.
However, in the coupling structure between the wheel bearing and the constant velocity joint in the related art, a predetermined clearance necessarily needs to be present between the teeth in order to couple the wheel hub and the constant velocity joint by means of the spline. As a result, there is a problem in that when a load, which is generated when the vehicle is driven, is applied to the coupling portion between the wheel hub and the constant velocity joint, the clearance is increased, noise is generated, a degree of design freedom deteriorates due to the spline coupling portion, and weight reduction is difficult to be realized due to the spline coupling portion of the constant velocity joint.